Heavy-duty "Dyna-Tred" swivel caster. 4 in. diameter. Steel plate with total lock braking system. The Total Lock braking system, designed for ease of operation, locks both the wheel and the swivel (standard on Dyna-Tred blue wheel). Metal protective thread guards. Two full independent rows of hardened, polished precision ball bearings roll freely in large-diameter, lubricated raceways. Fully seated wheel roller bearings eliminate the need for lubricating axle and reduces maintenance costs. Corrosion-resistant zinc finish. Load capacity: 300 lb. Sold by the unit.